Sense amplifiers usually use a pre-charge circuit, which, in many situations, are not process tracking and thus cause slower access in some operation corners. An operation corner refers to a device/transistor having a dopant type (e.g., N, P implants) biased by a process (e.g., fast N, slow P; fast P, slow N, etc) and operating at a particular temperature and/or voltage level (e.g., normal, low, or high Vdd, etc.). Further, the pre-charge voltage of the amplifier is generally fixed by the process, and is therefore not adjustable.
In an approach, to increase the access time, the pre-charge bias (e.g., pre-charge voltage) is raised to the operation voltage (e.g., Vdd) minus the threshold voltage of the transistors used in the circuit (e.g., Vt). This voltage Vdd−Vt, however, can be a limitation under some circumstances. Further, at different process corners, the pre-charge circuit comprising two serial N transistors does not track the sensing inverter comprising a P transistor in series with an N transistor. As a result, the sense amplifier behaves differently for different speeds of the different dopant types because the voltage level that changes the output logic of the inverter (e.g., the trip point) varies depending on the different process corners.
In another approach that uses a p-type Field Effect Transistor (pFET) in the pre-charge circuit, the pre-charge bias depends on the loading of a bit line (e.g., the BL loading). Inaccurate BL loading estimation, however, can affect the read access. For example, an over-charged bias because of an inaccurate BL loading estimation can cause a slower reading of the data with the current flowing when the memory is accessed, while an under-estimated BL loading can cause a slower reading of the data with small or no current flowing.
Like reference symbols in the various drawings indicate like elements.